The present invention relates to the electroless depositing of nickel coatings onto substrate surfaces and, more particularly, to a method and composition for use in obtaining bright nickel deposits on substrate surfaces by means of electroless depositing.
The electroless deposition of metals such as nickel or copper or alloys thereof onto the surfaces of both conductive (metal) or non-conductive substrates has been known and practiced for some time now. The most commonly practiced method of electroless deposition involves chemical reduction, i.e., wherein deposition takes place by the action of a reducing agent on dissolved metal in the presence of a substrate composed of an inherently catalytic material or a substance catalyzed by some form of pretreatment.
The essential principles of electroless deposition of nickel or nickel alloys are described in a number of patents and publications. Illustrative references include U.S. Pat. Nos. 2,532,283; 2,658,839; 2,658,841 and 2,658,842 and a 1954 review or Brenner, entitled "Electroless Plating Comes Of Age", Metal Finishing, December 1954, pp. 61 through 76, all of which are expressly incorporated herein by reference. Essentially, the bath or solution employed in electroless nickel depositing includes a soluble source of nickel ions, a reducing agent such as a hypophosphite compound, a complexing agent to prevent precipitation of metal ions from solution aand an acid or alkaline pH adjusting compound (including optional buffering compounds).
Electroless nickel bath or solutions of this type result in the depositing of a dull nickel coating on the substrate surfaces. Proposals have been maade for the inclusion in the plating solution of small amounts of metals such as lead, bismuth, antimony, molybdenum and the like to provide a brighter nickel deposit. Solutions such as these, when used to plate substrates such as rolled or cast steel, aluminum and the like, produce a nickel coating which is grainy and which may appear lustrous. However, for decorative applications on a buffed surface, the nickel deposit generally appears hazy or cloudy rather than specular as a mirror.